Piezo electric crystal control system



sept. 6, 1932. A, H TAYLOR 1,875,953

PIEZO ELECTRIC CRYSTAL CONTROL SYSTEM Filed Jan. 25, 1926' Il 1l 7 IN V EN TOR.

ATTORNEY Patented Sept. 6, 1932 UNITED s'nvlfas4 PATENT OFFICE ALBERT II. TAYLoa, `or WASHINGTON, DISTRICT or COLUMBIA, AssIGNoa, BY MESNE ASSIGNMENTS, To wIlaED laAzDIo, INC., oF NEW- Yoax, N. Y., A ConPoaATIoN or DELAWARE rIzojELECTnIC CRYSTAL CONTROL SYSTEM Application mea January as, 192e. smal No; 83,407.

My invention relatesbroadly to piezo electric frequency control systems, and more particularly to a system for controllin the temperature of piezoelectric crystals uring the operation thereof in anelectron tubewoscillation system.

One of the objects of my invention is to provide a system for maintaining the operating temperature of 'a piezo electric'crystal within definite limits for controlling the operation of an electron tube oscillator at constant frequency.

Another object of my invention is to provide means whereby a piezo electricv crystal may directly control relatively large'power output without the employment of a large number of stages of electron tube amplifiers in association therewith.

S'till another object of my invention is to provide means for protecting a piezo electric crystal against destruction from excessive inherent heating during its operation in an electron tube oscillating system for preservin g the structure of the crystal and maintaining permanent operation of the electron tube oscillator.

I have discovered that the influence of temperature on piezo velectric crystals becomes more and more important asthe frequencies at which the crystals are operatedare increased from five hundred kilocycles upwards, and it is necessary for constant vfrequency operation to maintain the operating temperatures of the crystals within certain limits. y

There is, however, another reason for providing control of temperature for piezo electric crystals used for the control of'radio frequencies. It is desirable to control'direct- 40 ly with the crystal as largey an output as possible in order to avoid the use of amplifiers in an excessive number of stages. When it is attemptedto control energies in excess of ten or fifteen watts of radio frequencies by piezo electric crystal action without the use ofampliiers, `it frequently happens that the crystal ceases to oscillate and an examination of the same will show that the crystal has become seriously heated, sometimes so much so as tofbe uncomfortably warmtothe touch and flaws have developed in the crystal which are sometimesin the nature of small punctures, sometimes in the nature of cracks with white snowy edges as if the structure had been pulverized in the vicinity of the crack, and sometimes the crystal will throw 0E particles on the side or edges of theV crystal which invariably impair the action of the crystal. An extended study of the crystal when crowded to :outputs between and 100 watts, that is, when controlling transmitting tubes without intermediate amplification so that 50to 100 watts radio frequency energy is developed has ,shown that the output can be materially increased if the crystal is maintained at a lower tem erature and,fin general, that if .the surroun ings of the crystal are such as to easily radiate any heating which has developed inthe crystal and passed kon by it tothe contact plates can escape, the crystal can be operated with greater output than whenno special means of cooling'is provided. This heating of thepiezo electric Icrystal is apparently due to two things: First, internal work due to the mechanical vibration of the crystal which increases rapidly as the elastic limit of the crystal is approached, that is, as the oscillations become more and more violent; and second, heating due to brushing. Electrically, the piezo electric crystal behaves in the circuit like a very large inductance in serieswith two very small capacities, one on the upper end of 'the inductance and one on the lower end of it.

The voltage over such an inductance may be very high. The voltage over the capacities at top and bottom of the inductance, considered in series with the inductance, may be high also, but the sum of the two voltages `which is what one measures with a'voltmeter connected between the top plate of a crystal oscillator and the bottom plate, is relatively low beca-use the two voltages under discussion are nearly 150 degrees out of phase with each other. The voltages over the large inductance which parallels in this analogy the interior of the crystal, corresponds to the high piezo electric strain within the crystal and the relatively high voltage between the crystal plate and the surface of the crystal, and which can not be measured by ordinary instruments at all because there is no way of connecting a Contact with the crystal surface to iii-usure the voltage, is responsible for brushing. Brushing normally never occurs through the crystal but rather from the top or bottom plate to adjacent crystal surface. It is diicult to determine which of the two effects, internal strain producing excessive internal work, or brushing, is mostly responsible for the heat developed in the crystal; but I have determined that if this heating is allowed to readily escape the crystal can be worked to higher output.

The invention by which I maintain the temperature of piezo electric crystals within certain limits will be more fully understood from the following specification by reference to the accompanying drawing, in which:

iigure 1 diagrammatically illustrates a cooling system for a piezo electric crystal arranged to control the operating characteristics of an electron tube oscillator; and Fig. 2 shows a modified form of cooling system for piezo electric crystals in the control circuit of an electron tube oscillator.

Referring to the drawing in more detail, an electron tube 1 has been illustrated having iilament, grid and plate electrodes la, 1b, and 1c. An inputcircuit 2 is provided in connection with the tube and an output circuit 3 connects between the plate electrode 10 and filament electrode 1a. Shunted across the input circuit 2, I provide a choke coil 4 and a batteri,Y system 5 for impressing a negative charge on the plate T which contacts with the upper surface of piezo electric crystal 6. The piezo electric crystal G rests upon a hollow plate structure S through which a cooling fluid, such as water or any other suitable liquid, is circulated by means of a pump system 15. The pump 15 has an inlet 14 connected to cooling tank or reservoir 9 from which the fluid is pumped through outlet 13, pipe connection 12 to hollow portion 11 of plate 8, and returned through pipeline 10 to cooling tank 9. The hollow plate 8 may be suitably insulated from the water circulating system by sections of insulated pipe for avoiding undesired capacity effects. A thermostatic control 18 may project into the cooling water in hollow plate 11 for controlling the operation of a driving motor 16 through connections emanating from terminal box 17 and power supply line 19. The driving motor 16 drives the water-circulating pump 15. The cooling tank 9 will normally have a temperature below the designated temperature for which the crystal is calibrated and known to have a designated frequency. This arrangement will not only prevent excessive rises in the crystal temperature permitting higher energy operation, but will exercise a positive control over the temperature, thus regulating the frequency with extreme accuracy.

The cathode structure 1a of electron tube l is heated from a suitable source, such as indicated at 23, controlled by rheostat 24:. The output circuit 3 contains inductance 20 and tuning condenser 21 with source of high potential supply 22 in circuit therewith with meters in the output circuit for determining the operating characteristics of the tube.

In Fig. 2 I have represented a circuit in which the piezo electric crystal 6 is mounted adjacent a plate structure 25 which is readily air-cooled by natural circulation of air over cooling vanes 26 of said plate. This cooling structure utilizes the principle of heat convection just as does the species of the invention shown in Fig. 1, the chief diierence being as between convection by air in the one case and by a liquid in the other' case.

While dissipation of heat generated by the crystal 6 is more efective when cooling vanes are provided on the under plate because of the weight of the crystal thereupon and the consequently greater heat conductivity between the crystal and the plate, it is not essentialto the carrying out of my invention that the crystal should be superposed on the means for dissipating the heat.

I have illustrated only two methods of cooling the plates which are in contact with the piezo electric crystal, but it will be understood that many modified forms may be employed and that the methods illust-rated herein merely set forth the principle of the invention and no limitations are intended upon the invention other than are imposed by the scope of the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States is as follows:

1. A piezo electric crystal control system comprislng a pair of contact plates, a piezo electric crystal mounted between said contact plates, and means for circulating a cooling fluid over at least one of said Contact plates, said cooling fluid being maintained at a temperature below that temperature at which the operating characteristics of said piezo electric crystal are impaired.

2. Piezo electric crystal apparatus comprising a support for a piezo electric crystal element, said support including a pair of parallel electrodes, a piezo electric crystal element mounted between said electrodes, one of said electrodes being provided with a hollow metallic jacket at one side thereof and means for circulating a cooling fluid through said jacket for extracting heat from said electrodes.

U 3. Piezo electric crystal apparatus comprising a substantially flat conductive plate member, a fluid jacket located on said plate member, a fluid inlet for said jacket and a fluid outlet for said jacket, a piezo electric crystal element mounted upon said conductive plate member, another electrode touching another surface of said piezo electric crystal element, said conductive surface bein maintained at a uniform temperature by t e ypassage of cooling fluid from said fluid inlet to said fluid outlet for conveying away heat generated by the movement of said piezo electric crystal element.

4. Piezo electric crystal apparatus comprising a pair of conductive electrodes, a piezo electric crystal element mounted between said electrodes, one of said electrodes having a substantially hollow construction, a fluid inlet adjacent one end of said hollow electrode, a fluid outlet adjacent the opposite end of the hollow electrode for the passage of a cooling fluid in contact with the under surface of said electrode for maintaining the contact surface of said electrode at a uniform temperature independent of the generation of heat under condition of rapid mechanical vibrations of said piezo electric crystal element.

5. A piezoelectric control system comprising a pair of contact plates, a piezo electric crystal mounted between said contact plates and means for circulating a cooling fluid through one of ksaid contact plates for eX- tracting heat generated by the mechanical vibration of said piezo electric crystal conducted to said contact plate, said means including one of said contact plates forming a fluid conductor.

6. A piezo electric crystal temperature conplates, a piezo electric crystal mounted between said plates, and means for maintaining said crystal at a constant temperature, said means including one of said contact plates having a fluid conductor.

7. In a piezo electric crystal control system comprising, a pair of contact plates, a piezo electric crystal mounted therebetween, a fluid conductor in one of said plates, a circulatory fluid system, means for operating said circulatory system, and thermostatic means associated with said fluid conductor contact plate for controlling the operation of said circulatory system and maintaining said crystal at a constant temperature.

8. A piezo electric crystal temperature controlled system comprising a pair of contact plates, a piezo electric crystal mounted between said plates and means for maintaining said crystal at a constant temperature, said trol system comprising a. pair of contact 

